The present invention pertains to a vehicle that is driven by an internal-combustion and/or electric engine, and comprises two front rolling and steering wheels and at least one rear driving wheel.
Prior art that can be considered as coming closest to the present invention is international patent application WO-A-99 41 136. In a three-wheel vehicle described therein, a linkage mechanism used to connect two front wheels with each other consists of two deformable trapeziums that, further to rigid members supporting spindles, is formed from two overlying pairs of cross arms provided with two articulated central fulcra.
To one of such pairs of cross arms, and therefore without any connection to a chassis of the vehicle, there are attached two end portions of a transverse shock-absorbing strut that comes into action when one of the two front wheels rises with respect to the other one.
To the contrary, when a driver forces the two front wheels to roll because of a simple displacement of his body (as in a two-wheel motor-cycle), for instance when taking a bend, the shock-absorbing strut is not subject to compression or relieving. The two central fulcra are in fact displaced with respect to a median longitudinal plane of the vehicle, but in each trapezium corresponding arms of the deformable trapeziums do not change their relative angle (to the contrary, they remain parallel to each other) and a center of gravity of the vehicle lowers as a function of solely a rolling angle, just as this occurs in a two-wheel vehicle. Transverse stability of the vehicle is ensured by the fact that steering axes, at Hooke""s joints connecting spindles to a steering assembly, remain constantly perpendicular to axes of rotation of the respective front wheels.
Because of absence of any connection between the shock-absorbing strut and the chassis, as well as considerable inertia of parts forming the linkage mechanism with respect to axes of the two central fulcra of the cross arms, this prior-art vehicle tends to be rather slow in responding to commands of a driver, so that it is actually rather difficult to drive. This is practically prejudicial to a possibility of equipping the vehicle, even and much more so on an optional basis, with a protective covering or a roll bar due to difficulty found by a design engineer to anticipate or predict all possible states of the vehicle when the front wheels thereof are rolling. Furthermore, an unavoidable presence of a bottom cross arm between equatorial planes of the front wheels and the respective steering axes thereof may have adverse consequences in a case of sharp braking, because of link rods of the steering assembly becoming greatly stressed thereby.
It therefore is a main purpose of the present invention to provide a vehicle with two front rolling and steering wheels, which, further to ensuring a greater extent of comfort as compared with a traditional motor-cycle, is free from the above drawbacks and is therefore capable of being equipped, even on an optional basis, with various types of protective coverings or roll bars. A further purpose of the present invention is to provide, albeit within certain limits, a simple and low-cost construction of the vehicle as compared to a traditional construction of two-wheel vehicles.
According to the present invention, these and further aims are reached in a vehicle having characteristics as recited in the appended claims, which vehicle uses a pair of shock-absorbing struts and an associated rocker-arm structure through which a chassis supports a cross-bar linkage mechanism that connects two front rolling and steering wheels to each other.
In this connection, the Applicant does not consider such prior publications as the U.S. Pat. Nos. 4,003,443, 4,887,829, 5,611,555, as well as patent applications WO-A-97 27 071, WO-A-98 43 872, as being of any relevance since, in vehicles having a single front steering wheel, shock-absorbing struts are featured which are associated with more or less horizontal fork members supporting two rear rolling, but not steering wheels.
In any event, features and advantages of the present invention will be more readily understood from a description that follows by way of non-limiting examples with reference to accompanying drawings, in which it should be noticed that, for reasons of greater simplicity, both the description and the drawings are substantially limited to those construction parts of a vehicle which are directly concerned with the present invention or are in any way useful in view of being able to explain a manner by which the invention actually works. As a result, references to other component parts (such as for instance driving engine, tanks, radiator, electric components, steering assembly and the like), which may be of a fully traditional type, are intentionally omitted.